RECORD: Darwin, C. R. 1837. On certain areas of elevation and subsidence in the Pacific and Indian oceans, as deduced from the study of coral formations. [Read 31 May] Proceedings of the Geological Society of London 2: 552-554.

"On certain areas of elevation and subsidence in the Pacific and
Indian oceans, as deduced from the study of Coral Formations;" by
Charles Darwin, Esq., F.G.S.

The author commenced by observing on some of the most remarkable
points in the structure of Lagoon islands. He then proceeded to show
that the lamelliform corals, the only efficient agents in forming a
reef, do not grow at any great depths; and that beyond twelve fathoms
the bottom generally consists of calcareous sand, or of masses of dead
coral rock. As long as Lagoon islands were considered the only
difficulty to be solved, the belief that corals constructed their
habitations (or speaking more correctly, their skeletons), on the
crests of submarine craters, was both plausible and very ingenious;
although the immense size, sinuous outline, and great number, must have
startled any one who adopted this theory. Mr. Darwin remarked that a
class of reefs which he calls "encircling" are quite, if not more,
extraordinary. These form a ring round mountainous islands, at the
distance of two and three miles from the shore; rising on the outside
from a profoundly deep ocean, and separated from the land by a channel,
frequently about 200 and sometimes 300 feet deep. This structure as
observed by Balbi1 resembles a lagoon, or an atoll, surrounding another
island. In this case it is impossible, on account of the nature of the
central mass, to consider the reef as based on an external crater, or
on any accumulation of sediment; for such reefs encircle the submarine
prolongation of islands, as well as the islands themselves. Of this
case New Caledonia presents an extraordinary instance, the double line
of reef extending 140 miles beyond the island. Again the Barrier reef,
running for nearly 1000 miles parallel to the North-East coast of
Australia, and including a wide and deep arm of the sea, forms a third
class, and is the grandest and most extraordinary coral formation in
the world.

The reef itself in the three classes, encircling, barrier and
lagoon, is most closely similar; the difference entirely lying in the
absence or presence of neighbouring land, and the relative position
which the reefs bear to it. The author particularly points out one
difficulty in understanding the structure in the barrier and encircling
classes, namely, that the reef extends so far from the shore, that a
line drawn perpendicularly from its outer edge down to the solid

rock on which the reef must be based, very far exceeds that small
limit at which corals can grow. A distinct class of reefs however
exists, which the author calls "fringing reefs," which extend only so
far from the shore, that there is no difficulty in understanding their
growth. The theory which Mr. Darwin then offered, so as to include
every kind of structure, is simply that as the land with the attached
reefs subsides very gradually from the action of subterranean causes,
the coral building polypi soon again raise their solid masses to the
level of the water; but not so with the land: each inch lost is
irreclaimably gone:—as the whole gradually sinks, the water gains foot
by foot on the shore, till the last and highest peak is finally
submerged. Before explaining this view in detail, the author offered
some considerations on the probability of general subsidences,—such as
the small portion of land in the Pacific, where many causes tend to its
production, an argument first suggested by Mr. Lyell, and the extreme
difficulty (with the knowledge that corals grow at but limited depths)
in explaining the existence of a vast number of reefs on one level,
without we grant subsidence, so that one mountain top should be
submerged after another; the zoophytes always bringing up their stony
masses to the surface of the water. Subsidence being thus rendered
almost necessary, it was shown by the aid of sections, that a simple
fringing reef would thus necessarily be converted by the upward growth
of the coral into one of the encircling order, and this finally, by the
disappearance through the agency of the same movement of the central
land, into a lagoon island. In the same manner a reef skirting a shore
would be changed into a barrier extending parallel to, but at some
distance from, the mainland.

Mr. Darwin then showed, that there existed every intermediate form
between a simple well characterized encircling reef, and a lagoon
island; that New Caledonia supplied a link between encircling and
barrier reefs; that the different reefs produced by the same order of
movement were always in juxtaposition, of which the Australian barrier
associated with encircled islets and true lagoons, affords a good
example. He then proceeded to show that within the lagoon of Keeling
Island, proofs of subsidence might be deduced from many falling trees
and a ruined storehouse; these movements appearing to take place at the
period of bad earthquakes, which likewise affect Sumatra, 600 miles
distant. It was thence inferred as probable, that as Sumatra rises, (of
which proofs are well known to exist,) the other end of the lever sinks
down; Keeling Island thus acting as an index of the movement of the
bottom of the Indian Ocean. Again at Vanikoro,1 where the structure
indicates according to the theory recent subsidence, violent
earthquakes are known lately to have occurred.

The author then removed an apparent objection to the theory, namely,
that subsidence would form a disc of coral but not a cup-shaped mass or
lagoon, by showing that the corals which grow in tranquil water are
very different from those on the outside, and less effective; and that
as the basin becomes shallower they are subject to various

causes of injury. The lagoon nevertheless is constantly filling up
to the height of lowest water spring tides, (the utmost possible limit
of living coral,) and in that state it long remains, for no means exist
to complete the work. Mr. Darwin then proceeded to the main object of
the paper, in showing that as continental elevations act over wide
areas, so might we suppose continental subsidences would do, and in
conformity to these views, that the Pacific and Indian seas could be
divided into symmetrical areas of the two kinds; the one sinking, as
deduced from the presence of encircling and barrier reefs, and lagoon
islands, and the other rising, as known from uplifted shells and
corals, and skirting reefs. The absence of lagoon islands in certain
wide tracts, such as in both the West and East Indies, Red Sea,
&c., was thus easily explained, for proofs of recent elevation are
there abundant. In a like manner, in very many cases where islands are
only fringed with reefs, which according to the theory had not been
subsiding, actual proofs of elevation were adduced. Mr. Darwin remarked
that, excepting on the theory of the configuration of reefs being
determined by the order of movement, the circumstance that certain
classes which are characteristic and universal in some parts of the
sea, being never found in others, is quite anomalous, and has never
been attempted to be explained.

Mr. Darwin then pointed out the above areas both in the Pacific and
Indian Oceans, and deduced the following as the principal results. 1st.
That linear spaces of great extent are undergoing movements of an
astonishing uniformity, and that the bands of elevation and subsidence
alternate. 2. From an extended examination, that the points of eruption
all fall on the areas of elevation. The author insisted on the
importance of this law, as thus affording some means of speculating,
wherever volcanic rocks occur, on the changes of level even during
ancient geological periods. 3. That certain coral formations acting as
monuments over subsided land, the geographical distribution of organic
beings (as consequent on geological changes as laid down by Mr. Lyell)
is elucidated, by the discovery of former centres whence the germs
could be disseminated. 4. That some degree of light might thus be
thrown on the question, whether certain groups of living beings
peculiar to small spots are the remnants of a former large population,
or a new one springing into existence.1 Lastly, when beholding more than
a hemisphere, divided into symmetrical areas, which within a limited
period of time have undergone certain known movements, we obtain some
insight into the system by which the crust of the globe is modified
during the endless cycle of changes.

1 This is Darwin's first published reference to his interest in the origin of species.